Absolute configuration of diterpenoids from Jatropha dioica by vibrational circular dichroism

Vibrational Circular Dichroism Absolute Configuration of Natural Products From 2015 to 2019

Although demonstrated in 1975, vibrational circular dichroism (VCD) finally started to popularize during this century as a reliable tool to determine the absolute configuration (AC) of organic molecules. This research field continues to be a very dynamic one, in particular for the study of natural products which are a unlimited source of chiral molecules. It therefore turns of interest to summarize the accomplishments published in recent years and to comment on some eventual difficulties that emerged in rare cases to complete the AC determination task. Therefore the aim of this review is to update VCD results for the AC assignment of natural products published from 2015 to 2019, a period in which VCD was reported in some 126 publications involving almost 300 molecules. They are organized according the type of studied metabolite allowing an easily search. The molecules correspond to 28 monoterpenes concerning 17 papers, to 42 sesquiterpenes in 14 papers, to 51 diterpenes in 19 publications, to 5 other terpenoids in three papers, to 48 aromatic molecules in 15 reports, to 20 polyketides in 10 publications, to 27 miscellaneous formulas also in 10 papers, and to 76 nitrogen containing compounds, which include alkaloids and their synthetic analogs, in 38 articles. The landscape of reviewed molecules is quite wide as it goes from simple monoterpenes, like borneol or camphor, to very relevant biological molecules like the alkaloid cocaine or tadalafil samples to distinguish genuine and counterfeit Cialis®. In addition, 5 natural products and a simple derivative published outside the reviewed period, were used to illustrate some aspects of density functional theory calculations.

The genus Jatropha (Euphorbiaceae): A review on secondary chemical metabolites and biological aspects

The genus Jatropha belongs to the Euphorbiaceae family and has about 175 species. Originally from tropical America, the Jatropha genus can be found all over the tropics and subtropics of Asia and Africa. Jatropha species are recognized to be important sources of secondary metabolites with a broad spectrum of biological functions. Extracts and isolated compounds from species of this genus have been known to have properties of cytotoxicity, antimicrobial, antifungal, anti-inflammatory, antioxidant, insecticidal, larvicidal, inhibition AChE, and toxicity activities. Investigations on the chemical aspects of the genus Jatropha have led to the identification of cyclic peptides, lignans, flavonoids, coumarins, alkaloids, eudesmenoic acids, and mainly terpenes. In this review, we provide a comprehensive picture of the phytochemical and biological characteristics of Jatropha species. The information gathered and approached in this paper might support the planning and discussion of future studies on the topic.

Vibrational optical activity for structural characterization of natural products

This review presents the recent progress towards elucidating the structures of chiral natural products and applications using vibrational optical activity (VOA) spectroscopy.

Absolute configuration of phomactatriene diterpenoids obtained by Wagner-Meerwein rearrangement of epimeric verticillols

The epimeric diterpenes (+)-(1S,3E,7E,11S,12S)-verticilla-3,7-dien-12-ol (1), isolated from Bursera suntui, and (+)-(1S,3E,7E,11S,12R)-verticilla-3,7-dien-12-ol (2), isolated from Bursera kerberi, gave the same Wagner-Meerwein rearrangement product (-)-(1E,4Z,8Z,11S,12R)-phomacta-1,(15)4,8-triene (3). The Et₂ O:BF₃ -induced transformations evidence that verticillenes and phomactanes, both containing the bicyclo[9.3.1]pentadecane skeleton, are biogenetically related through the verticillen-12-yl cation (A⁺ ), which also is a key intermediate in the biosynthetic pathways to generate antitumor taxanes. Molecular modeling using the Monte Carlo protocol, followed by density functional theory (DFT) geometry optimization employing the hybrid functionals B3LYP and B3PW91, both with the DGDZVP basis set, secured the configuration of 3 as followed from the good agreement between the calculated and experimental vibrational circular dichroism spectra. Similar DFT calculations allowed determining the absolute configuration of (+)-(1R,4R,5R,8S,9S,11S,12R,15R)-1,15:4,5:8,9-triepoxyphomactane (9), which surprisingly derives from epoxidation of the second minimum energy conformer of 3.

Constituents, Antioxidant and Antifungal Properties of Jatropha dioica var. dioica

The antioxidant and antifungal activity of n-hexane and ethyl acetate extracts of stems and roots of Jatropha dioica var. dioica, a plant species from the semi-arid regions of Hidalgo, Mexico, were evaluated by the 2,2-diphenyl-1-picrylhydrazyl and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) free-radical scavenging capacity assays and by growth inhibition of the phytopathogenic fungi, Alternaria alternata, Sclerotium rolfsii, Colletotrichum gloeosporioides, Rhizoctonia solani, and Fusarium oxysporum. The extracts exhibited a significant capacity to capture free radicals and a moderate capacity to inhibit fungal growth. A phytochemical study of these extracts led to the isolation of alkyl esters of acetic and ferulic acid, as well as the known diterpenes citlalitrione, jatrophatrione, jatropholone A, and jatropholone B, which were physically and spectroscopically characterized. These metabolites could be responsible for the observed antioxidant and fungicide activities of the extracts.

Diterpenoids of terrestrial origin

This review covers the isolation and chemistry of diterpenoids from terrestrial sources from 2017.

Stereochemistry of a Second Riolozane and Other Diterpenoids from Jatropha dioica

The dichloromethane extract of the roots of Jatropha dioica afforded riolozatrione (1) and a C-6 epimer of riolozatrione, 6-epi-riolozatrione (2), as a new structure and only the second reported riolozane diterpenoid. The two known diterpenoids jatrophatrione (3) and citlalitrione (4) were also isolated and characterized. Both epimers 1 and 2 are genuine plant constituents, with 2 likely being the biosynthesis precursor of 1 due to the tendency for the quantitative transformation of 2 into 1 under base catalysis. The structural characterization and distinction of the stereoisomers utilized ¹H iterative full-spin analysis, yielding complete J-correlation maps that were represented as quantum interaction and linkage tables. The absolute configuration of compounds 1-4 was established by means of vibrational circular dichroism and via X-ray diffraction analysis for 1, 2, and 4. Additionally, the cytotoxic and antiherpetic in vitro activities of the isolates were evaluated.

Chirality sensing of bioactive compounds with amino alcohol unit via circular dichroism

The aim of the present work was to test various chiroptical techniques, including in particular the in situ dirhodium methodology, to assign the absolute configuration of 1,2- and 1,3-amino alcohols. As models, we selected mainly compounds that have both an additional strongly absorbing and interfering chromophoric system and application in medicinal chemistry. Determination of the absolute configuration (AC) of the tested molecules such as cinchona alkaloids, Tamiflu, and others was carried out using a combination of electronic and vibrational circular dichroism (ECD, VCD) spectroscopy. It has been demonstrated that both 1,2- and 1,3-aminol moieties are subject to the same sector rule correlating stereostructure of formed Rh₂ -complex with chiroptical properties, and that the changes in the position of the stereogenic center do not affect its proper use.

Optimization of the Number of Considered Conformers for the Absolute Configuration Determination of Catechin and Epicatechin Peracetates by VCD

Epimeric catechin and epicatechin peracetates offer the possibility to explore the number of conformers needed for the absolute configuration determination without affecting the reliability of the assignment. Comparisons between experimental and DFT B3PW91/DGDZVP calculated curves showed that, in molecules where the conformational flexibility generates a large number of conformers, it is possible to significantly reduce the number of conformers needed to generate VCD results that provide secure absolute configuration assignment.